Thanks for reaching out.
From your heading, I am able to understand you are trying to integrate service now with Azure AD. To integrate with Service Now, you can add service now from list of SaaS application provided by Azure and configured as mentioned here.
However, on other hand to access the application registered in Azure AD, you already have the Global Administrator role which will allow to access all administrative features in Azure AD to manage users, groups and applications.
You can get the below details from the registered application as mentioned in screenshot:
1.Tenant ID/ Directory ID 2.Application ID/Client ID 3.Client Secret Key 4.Client Secret Value
To get the client key/value, you need to add new client secret and copy the value of the client secret which is no longer seen after you refresh the page and then you can use these values further.
Hope this will help. If you have any other question related to this, let us know.
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